1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device with improved luminance.
2. Discussion of the Related Art
An LCD device can realize low power consumption owing to a low driving voltage, and the LCD device is suitable for a portable. In this respect, the LCD device is widely used in various fields of notebook computer, monitor, spacecraft, aircraft, and etc.
The LCD device includes a lower substrate, an upper substrate, and a liquid crystal layer between the lower and upper substrates. In case of the LCD device, an alignment state of liquid crystal molecules in the liquid crystal layer is controlled based on whether or not an electric field is applied thereto, and light transmittance is controlled according to the alignment state of liquid crystal molecules, whereby images are displayed thereon.
Hereinafter, a related art LCD device will be described with reference to the accompanying drawings.
FIG. 1 is a cross section view illustrating the related art LCD device.
As shown in FIG. 1, the related art LCD device includes a liquid crystal panel 10 and a backlight unit 50.
The liquid crystal panel 10 includes an upper substrate 20, a lower substrate 30, and a liquid crystal layer 40 between the upper and lower substrates 20 and 30.
On the upper substrate 20, there is a light-shielding layer 22 to prevent light leakage. Then, respective red (R), green (G), and blue (B) color filters 24a, 24b, and 24c are formed between each light-shielding layer 22. A common electrode 26 is formed on the color filters 24a, 24b, and 24c. 
Although not shown, a thin film transistor and a pixel electrode are formed on the lower substrate 30, wherein the thin film transistor functions as a switching element, and the pixel electrode is electrically connected to the thin film transistor.
The backlight unit 50 supplies light to the liquid crystal panel 10. The backlight unit 50 is positioned under the liquid crystal panel 10. Although not shown, the backlight unit 50 includes a light source and various elements, for example, light-guiding plate and diffusion sheets to provide light supplied from the light source to the liquid crystal panel 10, uniformly.
In the related art LCD device, an alignment state of liquid crystal molecules in the liquid crystal layer 40 is controlled based on whether or not an electric field is applied thereto, and light transmittance is controlled according to the alignment state of liquid crystal molecules, whereby images are displayed thereon. Especially, various colors can be displayed according as light passes through the red (R), green (G), and blue (B) color filters 24a, 24b, and 24c. 
However, some of the light supplied from the backlight unit 50 is used to display the images on the related art LCD device, and a lot of the light supplied from the backlight unit 50 is lost. That is, the related art LCD device has a problem of low luminance caused by the low light transmittance.
The light transmittance in the related art LCD device might be lowered by various causes. Thus, there are continuous researches and studies for finding out the causes of low light transmittance, and overcoming the found causes. A method is to prevent the light transmittance from being lowered by the color filters 24a, 24b, and 24c. That is, the various colors are displayed according as the light supplied from the backlight unit 50 passes through the aforementioned color filters 24a, 24b, and 24c of the liquid crystal panel 10. At this time, a considerable amount of light is absorbed into the color filters 24a, 24b, and 24c, and some of the light is used to display the images.
The color filters 24a, 24b, and 24c are necessary for realization of the various colors. However, the light transmittance is lowered due to the color filters 24a, 24b, and 24c. Thus, a spectral apparatus is used to divide the light supplied from the backlight unit 50 into red (R), green (G), and blue (B) colors, and to supply them to the liquid crystal panel 10. This method enables to display the various colors without using the color filters. Even though the method using the spectral apparatus improves the luminance property by preventing the light transmittance from being lowered, desired colors cannot be realized due to difficulties in process, to thereby lower picture quality.
Thus, it is necessary to study and develop a method for minimizing the lowering of light transmittance by the color filters under the circumstance that the three color filter of red (R), green (G), and blue (B) color filters 24a, 24b, and 24c are used in the LCD device.